Transmission system



Patented Mar. 30, 1943 UNTED ST.

TRANSMISSION SYSTEM Frank A. Leibe, Quakertown, Pa., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 3, 1940, Serial No. 343,711

2 Claims.

This invention relates to a transmission system and more particularly to a transmission system utilizing unattended repeater stations.

An object of the invention is to facilitate supervision of a transmission system which involves unattended stations.

A more specic object of the invention is to provide an indication at an attended repeater station of the degree of efliciency with which a remote unattended repeater station is operating.

It is customary in modern transmission systems, particularly those involving a large number of signal channels such as a coaxial cable system, to provide a large number of line repeaters in tandem spaced at intervals which may be as short as llve miles or even less, with several unattended repeater stations between atten-ded stations; a section between two attended repeater stations may be from fifty to one hundred miles in length. While repeater equipment is now availavle which is suiciently reliable in its operation to justify this practice of leaving the majority of the repeater stations unattended, the possibility of an occasional decrease in operating efficiency of an unattended station to an undesirable point can never be entirely ruled out. It is desirable, therefore, that means be provided at the attended stations whereby the operating condition of the group of unattended stations to be supervised therefrom may be readily determined whenever desired without interrupting the normal use of the transmission system.

In accordance with the general method of operation of the supervising system contemplated by the present invention, a pilot frequency is applied to the transmission line and a portion of this pilot frequency leaving the line amplifier of the repeater station being tested is selected by a filter and utilized to control the energy of a signal transmitted over an auxiliary circuit to the attended station.

Full understanding of the arrangement contemplated by the present invention and appreciation of the valuablefeatures thereof will be gained from consideration of the following detailed description `in connection with the drawing, in which:

Fig. l illustrates schematically a portion of a coaxial transmission system provided with supervisory means utilizing features of the present invention;

Fig. 2'illustrates a similar portion of a transmission system provided with a different type of supervising meansyand y Fife 3 illustrates a Similar genion of v a ltrans- (Cl. 17g-175.31)

mission system provided with still another type of supervising means.

Referring now to Fig. 1. there is illustrated schematically portions of the equipment of attended repeater station A and unattended repeater stations U-I and U2 of a .system for transmitting signals over coaxial cable II in the direction indicated by the arrow. It` will be assumed that unattended stations U-I and U2 are included in the group of unattended stations arranged to be supervised from attended station A. It will be assumed also that a pilot current of predetermined frequency is applied to line II as well as message currents.

Filter I2 is connected across the output of line amplifier I3 of station U-I, this filter being de-V signed to pass a narrow band of frequencies which includes the pilot frequency. lA similar filter i4 is connected across the output of line amplifier I5 of station U-Z, this filter having the same pass-band as filter I2. Y

The output of filter I2, after amplification by auxiliary amplifier I6, is applied to constant-frequency oscillator I'I which is arranged to produce a wave of frequency f1; the output of oscillator Il is connected across the auxiliary signaling lin-e 2l. The amplitude of the wave of frequency f1 produced by oscillator Il and applied to line 2| is dependent upon the output of auxiliary amplifier I6, which depends, in turn, on the operating efficiency of line amplifier I3 in acting on the pilot frequency.

The output of filter I4, after amplification by auxiliary amplifier 22, is applied to constant-frequency oscillator 23 which is arranged to produce a wave of frequency f2; the output of oscillator 23 is connected across the auxiliary signaling'line 2|. The amplitude of the wave of frequency f2 produced by oscillator 23 is dependent upon the output of auxiliary amplifier 22 which depends, in turn, on. the operating eiciency of line amplifier I5 in acting on the pilot frequency.

A suitable amplitude measuring device 24 is provided at attended station I I, being connected to auxiliary line 2l through connecting lines 4l and 42. The connection through line 4I may be completed by closing switch 43; this connection includes band-pass filter 44 which is designed to pass a narrow band of frequencies which includes f1, the frequency produced by oscillator Il. The connection through line 42 may be completed by closing switch 45; this connection includes bandpass filter 46 which is designed to pass a narrow band of frequencies which includes f2, the frequency produced by oscillator 23.

Now in order to obtain at station A an indication of the degree of efficiency with which line amplifier I3 of unattended repeater station U-I is operating, it is merely necessary to close switch 43 whereupon the wave of frequency f1 produced by oscillator II and applied to line 2l Will be applied over line 4I to amplitude measuring device 24, filter 44 being designed, as above stated, to pass a narrow band of frequencies which includes the frequency fi. As previously brought out the amplitude of the wave f1, produced by oscillator I'I, is dependent upon the output of auxiliary amplifier I5 which, in turn, is dependent upon the output of line amplifier I3 so that the reading of amplitude measuring device 24 will be a direct indication of the efficiency with which line amplifier I3 is operating.

Similarly, in order to obtain indication of the degree of efliciency with which line amplifier I5 of unattended repeater station U- is operating,

it is merely necessary to close switch whereupon the wave of frequency f2 produced by osci1 lator 23 and applied to auxiliary signaling line 2| will be supplied to amplitude measuring device 24 over line 42, filter 46, as above stated, being designed to pass a narrow band of frequencies which includes the frequency f2. Under these conditions the reading of amplitude measuring device 24 will be direct indication of the degree of efficiency with which line amplifier I 5 is operating.

It is obvious that more unattended stations than the two illustrated in Fig. 1 may be supervised from station A, it being necessary merely to assign a different test frequency (corresponding to frequency f1 of station UI and f2 of station U-2) to each station and to provide an additional selective path (corresponding to lines 4I and 42) at station A for each additional test frequency assigned. v

Referring now to Fig. 2, there is illustrated schematically portions of the equipment of attended repeater station B and unattended repeater stations U-3 and U-4 of a system for transmitting signals over coaxial line 5I in the direction indicated by the arrow. It will be assumed that unattended repeater stations U-Zi and U-4 are included in the group of unattended stations arranged to be supervised from attended station B. It will be assumed also that apilot current of predetermined frequency is applied to line 5I as well as the message currents.

Two constant frequency oscillators, 52 and 53, are provided at station A; oscillator 52 produces a fixed frequency f1 and its output may be applied to auxiliary signaling line 51 by 'closing switch 54 while oscillator 53 produces a fixed frequency f2 and its output may be applied to the auxiliary signaling line by closing switch '55. A direct current meter 55 is also provided at station B, being connected across auxiliary signaling line 51.

A filter II is connected across the output of line amplifier 12 of unattended station U3; this filter is designed to pass a narrow band of frequencies which includes the pilot frequency. A second filter, 73, is connected across auxiliary signaling line 5l, this filter being designed to pass a narrow band of frequencies which Vincludes the frequency f1 produced by oscillator 52. The output of filter 'I3 is connected through the opera-ting winding of alternating current relay '24, while the output of filter 'Il Vis connected to iliary amplier 'I5 and 'rectifier bridge 1S.

Filter 8|, which is connected across the output of line amplifier 82 of unattended repeater station U-4, is designed to pass the same narrow band of frequencies as filter 'II which band, as previously stated, includes the pilot frequency. Filter 83 which is connected across auxiliary signaling line 51 is designed to pass a narrow band of frequencies which includes the frequency f2 produced by oscillator 53. The output of filter 83 is connected through the operating winding of alternating current relay twhile the output of filter 8I is connected to the two make contacts of the relay through auxiliary amplifier 85 and rectifier bridge 86. Low pass filters 9|, 92 and 93 are designed to permit passage of direct current and to prevent passage of frequencies fi and fz, thereby affording proper separation of the direct current and alternating current paths.

Assuming now that it be desired to obtain an indication at attended station B of the degree of efliciency with which line amplifier 'I2 of unattended station U-'3 is operating, switch 54 is closed, thereby applying current of frequency ,f1 to auxiliary line 5l. This current is passed by filter 'I3 and causes operation of relay 14. As previously pointed out, a pilot current is applied to the line at all testing periods and this pilot current is passed by filter il. Operation of relay 'I4 completes at the two make contacts thereof a path over which this pilot current, after ampliiication by amplifier 'I5 and rectification `by rectifier bridge 78 is applied to auxiliary signaling line 51 over which it is transmitted to attended station B. This current is measured by direct current meter 5S and the reading, after due allowance has been made for the known amplification factor of amplifier l5, will be an indica tion of the degree of efiiciency with which line amplifier 'I2 is operating.

The apparatus of unattended station U-4 is not affected by the above operation in View of the fact that the applied frequency f1 is not passed by filter 53. Should it be desired to observe the operation of line amplifier 82, switch 55 is closed, thereby applying current of frequency f2 to auxiliary line 57. This curreml is passed by filter 83 and causes operation of alternating current relay 8d. Operation of relay 3d connects the amplified and rectified pilot current passed by lter 8I to the auxiliary signaling line 5T over which it is transmitted to attended station B. This current is measured by meter 55, the reading of which provides an indication of the degree of efficiency with which amplifier 32 is operating.

While only two unattended repeater stations, U-3 and U-d, have been illustrated, it will be obvious that more than two unattended stations may be controlled from attended station B in a manner similar to that described, the equipment of the additional stations being similar'in general to that of the stations illustrated.

Referring now to Fig. 3 there is illustrated schematically portions of the equipment of attended repeater station C and unattended repeater stations U- vand U-t of a system for transmitting signals over coaxial line iDI in the direction indicated by the arrow, It will be assumed that unattended stations U-S and U- are included in the group of unattended stations arranged to be supervised from attended station C. It will be assumed also that a pilot current of predetermined frequency is applied to lline IDI as well as the message currents.

A direct current meter I2-and an indicator current of the saine frequency is transmitted Y `over the line for repeater energization, this current may be utilized for operation of the motors.r

Filter I I2 provided at unattended station U--5 is designed to pass a narrow band of frequencies which includes the pilot frequency. When brush 3 or" rotary distributor i is in engagement With conductive segments i It and H5 ofy the distributor commutator, the output of filter ||2, after amplification by auxiliary amplifier I IE and rectification by rectifier bridge is applied to auxiliary signaling line I 32.

Filter |33 of unattended station U-G is de-` signed to have the same pass band as filter H2, that is, it passes a narrow band of frequencies which includes the pilot frequency. When brush |34 of distributor I 06 is in engagement with conductive segments |35 and |35 of the distributor commutator, the output of filter |33,`after amplification by auxiliary amplifier |31 and rectification by rectier bridge |4| is applied to auxiliary signaling line |32.

Indicator |03, which as previously pointed out operates in synchronism with rotary distributors |05 and |05, is arranged to show which distributor is, at any given instant, in position to connect the output of an unattended station filter to line |32. For example, for the positions illustrated indicator |03 would show U-5. In the next interval when brush |34 contacted segments |35 and |36 it Would show "U-S and so on. At any given time the reading of meter |02 Will be, of course, an indication, after due allowance has been made for amplification by the local auxiliary amplifier, of the degree of efficiency With which the line amplifier of that unattended station flashed by indicator |03 is operating.

In order to bring indicator |03 and distributors |05 and |06 back into step should they get out of synchronism, latches |43, |44 and |45 may be pulled into position (by operation of respective relays |40, |41 and |6I over an obvious circuit completed by closing switch |62) to engage the respective rotating members and momentarily hold them al1 in the same relative position so that when released all will start from the same relative point. To permit this holding action the indicator and distributor arms are coupled to their respective motorsk by a friction drive.

It will be apparent, of course, that the group of unattended repeater stations supervised from attended station C may Well include more than the two stations illustrated and that the equipment of the additional stations will be similar in general to that of the stations illustrated.

In the use of the type of supervising system contemplated by the present invention it may be necessary in certain instances to modify the readings in view of temperature changes, i. e., in cases Where the talking pair is provided with regulating means to compensate for temperature changes While the auxiliary pair is not so compensated. For example, a chart may be provided to show necessary modifications of the readings for various temperatures and the resistance of the auxiliary pair may be measured to obtain an indication of the cable temperature. Suitable modifications of the readings may then be made.

While certain specific embodiments of the invention have been selected for detailed descrip tion, the invention is not, of course, limited in its application to these embodiments. The einbodiments described should be talren as illustrative of the invention and not as restrictive thereof.

What is claimed is:

l. In a signaling system, an attended station, a rst unattended repeater station and a second unattended repeater station, said unattended stations being geographically separated from said attended station and from each other, a

transmission line joining said attended station and said unattended stations, a line amplifier at each of said unattended stations, means at said attended station for applying a pilot current of predetermined frequency to said line, a shunt path at each of said unattended stations for diverting a portion of said pilot current of predetermined frequency after ampliiication by the respective line amplifier of the unattended station, a lter in each of said paths for excluding therefrom currents of other than said predetermined frequency, means at each of said unattended stations for rectifying the respective portion of said pilot current diverted through the shunt path of the respective unattended station, an auxiliary signaling line connecting said attended and said unattended stations, means connected to said auxiliary line at said attended station for indicating the energy of direct current signals received over said auxiliary line, means at each of said unattended stations for connecting the output of said rectifying means to said auxiliary line, and means at said attended station for selectively controlling the operation of said last-mentioned means at the unattended stations.

2. In a signaling system, an attended station, a plurality of unattended repeater stations geographically separated from said attended station and from each other, a transmission line joining said attended station and said unattended stations, an auxiliary line also joining said attended station and said unattended stations, means at said attended station for applyinga pilot current of predetermined frequency to said transmission line, means at each of said unattended stations for amplifying said pilot current, a shunt path at each of said unattended stations for diverting a portion of said pilot current after amplification by a respective one of said amplifying means, a lter in each of said paths for excluding therefrom currents of other than said predetermined frequency, means in each of said shunt paths for rectifying theV rent signals received over said auxiliary line from said unattended stations, and means for selectively connecting the outputs of each of said rectifying means to said auxiliary line.

FRANK A. LEIBE 

